Process for encasing an object



June 11, 1963 T. D. SHARPLES 3,0 0

PROCESS FOR ENCASING AN OBJECT Filed Jan. 7, 195a INVENT. THOMAS D. SHARPL.

ATTORNEY Patented June 11, I95? 3,63%,901 PROCES FGR ENCAEING AN OBJEQT Thomas D. Sharples, Plymouth Meeting, Pa, assignor to The Sharpies Corporation, a corporation of Delaware Filed Jan. 7, 1958, Ser. No. 707,640 18 Claims. (Cl. 29-52%) This invention relates generally to a process for encasing an object. The process may be used in the manufacture of many items. it is useful, for instance, in the manufacture of replaceable nozzle bushings for centrifuges, and it is in such use that it will hereinafter be described.

A type of centrifuge bowl adapted for the peripheral discharge of a separated heavy component is Provided with a plurality of nozzles spaced circumferentially about its periphery through which a separated heavy component flows continuously while the centrifuge is in operation. The continuous flow which frequently, though not necessarily, is of liquid intermixed with solids, causes Wear in the nozzle channel or opening, the rate of which being greatly increased when the material discharged is of an abrasive character.

The cross-sectional area of the channels in the discharge nozzles must, of necessity, be judiciously chosen for the particular type of separation to be made, as is Well understood in the centrifuging art, for the rate of discharge of heavy component in relation to the rate of feed is a factor entering into the control of the radial position of the interface between the light component and the next heavier component being separated, irrespective of the number of discharge streams, i.e. two or three. Since any wear in the channel results in its enlargement, it follows that replacement becomes necessary in the case of more than permissible Wear, so that the desired balance may be maintained in the centrifuge bowl between layers of components being separated.

The necessity for adapting the diameter of the nozzle channels to the particular separation to be made, as Well as the necessity for replacement following wear, has lead to the use of replaceable bushings or inserts which may be made with discharge channels of various diameters from which the proper selection may be made, either initially or for replacement purposes.

In view of the high centrifugal forces developed in centrifugal separations, such discharge channels, which usually are cylindrical in shape, are of necessity of very small diameter, e.g. from 0.830 or slightly less to 0.065 or slightly more, in order that the rate of discharge therethrough may be appropriately controlled.

Because of the problem of wear, the material from which nozzle bushings are made must of necessity be extremely hard in order that the Walls of the nozzle channel may have the required abrasion resistance. Nozzle bushings, therefore, are commonly made from materials such as cemented tungsten, carbide, high fired alumina, fused boron carbide and like very hard materials.

Formation of the channel is an operation obviously requiring a high degree of precision. It is performed by means well known in the art, and constitutes no part of the present invention.

The present invention pertains to contouring the outer circumferential surface of the nozzle bushing, which also is an operation requiring a high degree of precision, if leakage is to be avoided.

To illustrate, the outer circumferential surface of a typical nozzle bushing is commonly, though not necessarily, formed with a slight taper in the direction of the channel axis, and the nozzle bushing holder, i.e. the main body of the nozzle, is provided with a complementary taper, each so precisely formed that, when the bushing is inserted in place, it not only is held in appropriate position, no other securing mechanism being required, but its fit is such as to avoid leakage about the taper.

Typical nozzle bushings are usually, though not necessarily, generally cylindrical in shape when initially produced in the rough. In view of the extreme hardness of the material from which a nozzle bushing is made, the finishing of the outer circumferential surface thereof has heretofore been a time-consuming and expensive operation, for the more suitable a material of this type is for abrasion resistance the less suitable it is for this finishing operation.

This invention is more particularly directed to the shaping of the outer circumferential surface of a nozzle bushing to the desired dimensions, although the steps involved may have other applications.

I-leretofore the forming of the outer circumferential surface of a nozzle bushing to the desired outer dimensions and shape has required diificult machining, such as by diamond grinding, ultrasonic abrasion and/ or, in the case of conducting materials, by electro sparking.

in accordance with my invention, one or more nozzle bushings, usualiy a large number, are placed in a metal tube of the same or similar cross-sectional geometric shape and of somewhat greater diameter. The tube is then stretched lengthwise with consequent decrease in diameter with the result that each bushing becomes circumferentially encased in a tightly fitting section of the tube. The metal encasement of the bushing is now machined to size and shape which can be done far more readily than the machining of the original bushing.

Other features of the invention will become apparent to persons skilled in the art as this specification proceeds and upon reference to the drawings in which:

FIGURE 1 is a perspective view considerably enlarged of a typical nozzle bushing;

FiGURE 2 is a sectional elevation of a tube containing a plurality of nozzle bushings;

PlGURE 3 is a view partly in section illustrating the circumferential encasement with metal of bushings after elongation of the tube;

PTGURE 4 is illustrative of a modification;

FIGURE 5 is a sectional elevation of a finished encased nozzle;

FIGURE 6 illustrates a method for heating a tube prior to its elongation; and

FIGURE 7 is a sectional elevation of a modified encased nozzle.

Referring now more particularly to the drawings, at 10 in FIGURE 1 is illustrated a typical nozzle bushing having a tapered surface 11 and a discharge channel 12. FIGURE 1 has been considerably enlarged, for a commonly used nozzle bushing has a length of approximately and a diameter, whether the circumferential surface is cylindrical or tapered, of approximately average diameter in the case of a taper. The taper, when employed, is frequently so slight as to be almost imperceptible to the naked eye.

In FiGURE 2 is illustrated a tube i3 having a bore or channel 14 and containing a plurality of nozzle bushings 15 of somewhat lesser diameter than the bore 14, e.g. Upon elongation of the tube 13, such as by stretching upon engagement of the ends, and the application of tensile stresses in any desired manner by any means known in the art for which various well known tools are available, tube 13 takes the form shown in FIG- URE 3, wherein the portions of the tube 13 between the bushings 15 acquire a lesser diameter by necking of the tube 13 as illustrated (with exaggeration) at 16, the other portions of tube 13 tightly engaging the circumferential surfaces of the bushings 15.

The outer circumferential surface of each portion of the tube 13 which encases a bushing 15 may now be machined to a desired shape, means for which will become immediately apparent to persons skilled in the art. For instance, the entire tube may be set up in a lathe, and each individual outer surface of the tube portion encasing a bushing 15 brought to the desired shape with a suitable tool. Each individual encased bushing may then be severed from the tube by the use of a suitable cutting tool, and the ends of the encased bushing brought to any desired finish. On the other hand the stretched tube lengths containing a multiplicity of encased bushings 15 may be fed similar to bar stock through the head stock of a suitably tooled turret lathe, or automatic screw machine, for shaping the encasing metal about each individual bushing, including parting off of the finished pieces, as will be well understood by persons skilled in the art upon becoming familiar herewith.

A finished encased bushing 1'7 having a tapered outer surface 18 is illustrated in exaggerated scale in FIGURE 5.

By the use of a roller parting tool for cutting off the individual encased bushings, tubing metal may be rollburnished over the ends of the individual bushing. This is illustrated in FIGURE 7 wherein bushing 21 is shown as having an encasement 22 with ends 23 extending partially about the ends of the bushing 21.

A modification of the invention is illustrated in FIG- URE 4 wherein spacers 24 which are of lesser diameter than the bushings 15, are shown between individual bushings 15 in tube 13. The assembly of alternate bushings 15 and spacers 24 is made prior to the stretching of the tube 13. The result, with necked portions shown exaggerated for better illustration, is shown in FIGURE 4. A better control of the encasement of the individual bushings and of the degree, extent and shape of the necked portions is thus afforded, particularly when the tube 13 is stretched with all bushings and spacers in contact with each other. Other variations or modifications are possible.

Tube 13 preferably is of metal, e.g. of steel, nickel, chromium, aluminum, brass, or alloys thereof, although any other material capable of taking a permanent set upon stretching may be employed. Tube 13' also is preferably corrosion-resistant. Stainless steel is particularly suitable for the purpose, e.g. 316 stainless steel tubing having a wall thickness in the range of 0.015 to .030". Wall thickness is not critical, but usually will not be so thick as to make stretching inordinately difficult, nor so thin as to leave insuflicient metal for machining to shape.

The difference between the inside diameter of tube 13 and the outside diameter of bushings is not critical, although this difference is preferably maintained small to limit the extent of necessary stretching by elongation of the tube 13. Preferably this difference is maintained between a sliding fit and Ordinarily, the outside diameter of bushing 15 should be at least 75% of the interior diameter of tube 13.

In the case of bushings made from abrasion-resistant materials having brittle and/or lesser strength qualities, it is sometimes desirable to pretreat the bushings in an abrading mill with a wet charge of abrasive, e.g. 60 mesh silicon carbide, to round the edges of the bushings slightly, and then to encase the same as illustrated in FIG- URE 7. This decreases the chance of possible damage to the bushings resulting from handling and use. Such pretreatment also prepares the outer circumferential surface of the bushing for a leak-tight fit with the encasement with less stretch of tube 13 and thus less stress on the bushing, resulting in less breakage, irrespective of whether the encasement is brought around the edges as illustrated in FIGURE 7. This pretreatment may be employed, of course, irrespective of the strength or brittleness of the material from which the bushing is made.

Such pretreatment of the nozzle bushings prior to their encasement is helpful in all instances in which the outer circumferential surface of the bushing is rough which is not uncommon depending upon the method employed and care exercised during manufacture.

Another method for pretreating to facilitate the formation of a leak-proof joint between the bushing and the encasing metal is to pretreat the outer surface of the bushing, such as by gilding, e.g. with gold, or platinizing, to provide a layer of malleable or ductile metal, preferably corrosion-resistant, between the tube and the bushing, which acts much like a gasketing material between the tube and the bushing upon stretching of the tube.

As pointed out previously, the encasing metal may be of any desired thickness, and may be comprised of any suitable ductile material which is usually metal. In the case of tubes of metals which do not elongate readily, whether because of the nature of the metal or because of the thickness of the tube, heating of the tube may be resorted to in order to soften the tubular material and thus facilitate its elongation. Any desired suitable means may be employed for the heating of the tube, of which the passing of an electric current through the tube is an example. The latter is illustrated in FIGURE 6 in which tube 13 containing bushings 15 is shown as having terminals 26 and 27 to which are attached wires 28 and 29, respectively, which in turn lead to the movable member of a double pole single throw switch 3%. The stationary contacts 31 of the switch are connected to any suitable electrical source, not shown.

Many other variations in the practice of the invention will become apparent to persons skilled in the art upon becoming familiar herewith. Therefore, while I have particularly described my invention, it is to be understood that this is by way of illustration, and that changes, omissions, additions, substitutions and/ or other modifications may be made without departing from the spirit thereof. Accordingly, it is intended that the patent shall cover, by suitable expression in the claims, the various features of patentable novelty that reside in the invention.

I claim:

1. A process for encasing the outer peripheral surface of an object which comprises placing said object in a tube having its inner periphery of a cross-sectional geometrical shape generally corresponding to the cross-sectional geometrical shape of said object, said tube being of a ductile substance, thereafter elongating said tube by longitudinal stretching through engagement of said tube on opposite sides of said object to decrease its diameter with consequent peripheral shrinkage to cause said tube to grip the outer surface of said object, said longitudinal stretching being such as to cause said tube to neck on opposite sides of said object, and thereafter removing from said object undesired excess portions of said tube.

2. The process of claim 1 where said tube is of metal.

3. The process of claim 2 wherein a plurality of objects are placed in spaced relation in said tube prior to its elongation to produce a plurality of encased objects in a single operation.

4. The process of claim 3 wherein spacing members of lesser diameter than the objects are positioned between the objects in the tube prior to its elongation.

5. The process of claim 2 wherein the encasing metal is caused to overlap opposite ends of the object.

6. The process of claim 2 wherein the temperature of the tube is elevated sufiiciently to increase its ductility.

7. The process of claim 2 wherein the object is a nozzle bushing.

8. The process of claim 1 wherein the step of removing from the object undesired excess portions of the tube includes machining to a desired shape and dimension.

9. A process for encasing a plurality of objects in spaced relation within a metal tube having its inner periphery of a cross-sectional geometrical shape generally corresponding to the cross-sectional geometrical shape of said objects, which comprises placing said objects in said metal tube, elongating said tube by longitudinal stretching to decrease its diameter and engage said objects, further elongating said tube by stretching to cause necking of the tube at the spaces between said objects, said necking securing said objects in spaced relationship Within said tubes.

10. The process of claim 9 wherein the geometrical cross-sectional shape of the inner periphery of the tube and the geometrical cross'sectional shape of the objects are circular.

11. The process of claim 9 wherein the temperature of the tube is elevated sufficiently to increase its ductility.

12. The process of claim 9 wherein said objects are placed in said metal tube in spaced relation.

13. A process for encasing an object including the steps of placing a plurality of such objects in spaced relation in a tube of ductile material, stretching the tube longitudinally to reduce its diameter and engage the objects, further stretching the tube longitudinally to cause a necking of the tube in between objects, and severing the tube to produce the single encased object.

14. The process of claim 13 including the further step of removing from said object undesired excess portions of said tube.

15. The process of claim 13 including the additional step of causing the encasing material to overlap opposite ends of the object.

References Cited in the file of this patent UNITED STATES PATENTS 1,728,172 Bendix 'Sept."17, 1929 2,051,949 Inscho Aug. 25, 1936 2,131,766 Temple Oct. 4, 1938 2,137,537 McIntosh Nov. 22, 1938 2,219,434 White Oct. 29, 1940 2,386,747 Ris Oct. 16, 1945 2,398,364 Elfstrom Apr. 16, 1946 2,536,821 Rappl Jan. 2, l 2,607,109 Reynolds Aug. 19, 1952 2,874,459 Haldeman Feb. 24, 1959 

1. A PROCESS FOR ENCASING THE OUTER PERIPHERAL SURFACE OF AN OBJECT WHICH COMPRISES PLACING SAID OBJECT IN A TUBE HAVING ITS INNER PERIPHERY OF A CROSS-SECTIONAL GEOMETRICAL SHAPE GENERALLY CORRESPONDING TO THE CROSS-SECTIONAL GEOMETRICAL SHAPE OF SAID OBJECT, SAID TUBE BEING OF A DUCTILE SUBSTANCE, THEREAFTER ELONGATING SAID TUBE BY LONGITUDINAL STRETCHING THROUGH ENGAGEMENT OF SAID TUBE ON OPPOSITE SIDES OF SAID OBJECT TO DECREASE ITS DIAMETER WITH CONSEQUENT PERIPHERAL SHRINKAGE TO CAUSE 